/*
 * Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
 * project.
 */
/* ====================================================================
 * Copyright (c) 1999-2003 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    licensing@OpenSSL.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 *
 */
/* X509 v3 extension utilities */

#include <ctype.h>
#include <stdio.h>
#include <string.h>

#include <openssl/bn.h>
#include <openssl/bytestring.h>
#include <openssl/conf.h>
#include <openssl/err.h>
#include <openssl/mem.h>
#include <openssl/obj.h>
#include <openssl/x509.h>

#include "../conf/internal.h"
#include "../internal.h"
#include "internal.h"


static char *strip_spaces(char *name);
static int sk_strcmp(const char *const *a, const char *const *b);
static STACK_OF(OPENSSL_STRING) *get_email(const X509_NAME *name,
                                           const GENERAL_NAMES *gens);
static void str_free(OPENSSL_STRING str);
static int append_ia5(STACK_OF(OPENSSL_STRING) **sk,
                      const ASN1_IA5STRING *email);

static int ipv4_from_asc(unsigned char v4[4], const char *in);
static int ipv6_from_asc(unsigned char v6[16], const char *in);
static int ipv6_cb(const char *elem, size_t len, void *usr);
static int ipv6_hex(unsigned char *out, const char *in, size_t inlen);

// Add a CONF_VALUE name value pair to stack

static int x509V3_add_len_value(const char *name, const char *value,
                                size_t value_len, int omit_value,
                                STACK_OF(CONF_VALUE) **extlist) {
  CONF_VALUE *vtmp = NULL;
  char *tname = NULL, *tvalue = NULL;
  int extlist_was_null = *extlist == NULL;
  if (name && !(tname = OPENSSL_strdup(name))) {
    goto err;
  }
  if (!omit_value) {
    // |CONF_VALUE| cannot represent strings with NULs.
    if (OPENSSL_memchr(value, 0, value_len)) {
      OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_VALUE);
      goto err;
    }
    tvalue = OPENSSL_strndup(value, value_len);
    if (tvalue == NULL) {
      goto err;
    }
  }
  if (!(vtmp = CONF_VALUE_new())) {
    goto err;
  }
  if (!*extlist && !(*extlist = sk_CONF_VALUE_new_null())) {
    goto err;
  }
  vtmp->section = NULL;
  vtmp->name = tname;
  vtmp->value = tvalue;
  if (!sk_CONF_VALUE_push(*extlist, vtmp)) {
    goto err;
  }
  return 1;
err:
  if (extlist_was_null) {
    sk_CONF_VALUE_free(*extlist);
    *extlist = NULL;
  }
  OPENSSL_free(vtmp);
  OPENSSL_free(tname);
  OPENSSL_free(tvalue);
  return 0;
}

int X509V3_add_value(const char *name, const char *value,
                     STACK_OF(CONF_VALUE) **extlist) {
  return x509V3_add_len_value(name, value, value != NULL ? strlen(value) : 0,
                              /*omit_value=*/value == NULL, extlist);
}

int x509V3_add_value_asn1_string(const char *name, const ASN1_STRING *value,
                                 STACK_OF(CONF_VALUE) **extlist) {
  return x509V3_add_len_value(name, (const char *)value->data, value->length,
                              /*omit_value=*/0, extlist);
}

// Free function for STACK_OF(CONF_VALUE)

void X509V3_conf_free(CONF_VALUE *conf) {
  if (!conf) {
    return;
  }
  OPENSSL_free(conf->name);
  OPENSSL_free(conf->value);
  OPENSSL_free(conf->section);
  OPENSSL_free(conf);
}

int X509V3_add_value_bool(const char *name, int asn1_bool,
                          STACK_OF(CONF_VALUE) **extlist) {
  if (asn1_bool) {
    return X509V3_add_value(name, "TRUE", extlist);
  }
  return X509V3_add_value(name, "FALSE", extlist);
}

static char *bignum_to_string(const BIGNUM *bn) {
  char *tmp, *ret;
  size_t len;

  // Display large numbers in hex and small numbers in decimal. Converting to
  // decimal takes quadratic time and is no more useful than hex for large
  // numbers.
  if (BN_num_bits(bn) < 32) {
    return BN_bn2dec(bn);
  }

  tmp = BN_bn2hex(bn);
  if (tmp == NULL) {
    return NULL;
  }

  len = strlen(tmp) + 3;
  ret = OPENSSL_malloc(len);
  if (ret == NULL) {
    OPENSSL_free(tmp);
    return NULL;
  }

  // Prepend "0x", but place it after the "-" if negative.
  if (tmp[0] == '-') {
    OPENSSL_strlcpy(ret, "-0x", len);
    OPENSSL_strlcat(ret, tmp + 1, len);
  } else {
    OPENSSL_strlcpy(ret, "0x", len);
    OPENSSL_strlcat(ret, tmp, len);
  }
  OPENSSL_free(tmp);
  return ret;
}

char *i2s_ASN1_ENUMERATED(const X509V3_EXT_METHOD *method,
                          const ASN1_ENUMERATED *a) {
  BIGNUM *bntmp = NULL;
  char *strtmp = NULL;
  if (!a) {
    return NULL;
  }
  if (!(bntmp = ASN1_ENUMERATED_to_BN(a, NULL)) ||
      !(strtmp = bignum_to_string(bntmp))) {
  }
  BN_free(bntmp);
  return strtmp;
}

char *i2s_ASN1_INTEGER(const X509V3_EXT_METHOD *method, const ASN1_INTEGER *a) {
  BIGNUM *bntmp = NULL;
  char *strtmp = NULL;
  if (!a) {
    return NULL;
  }
  if (!(bntmp = ASN1_INTEGER_to_BN(a, NULL)) ||
      !(strtmp = bignum_to_string(bntmp))) {
  }
  BN_free(bntmp);
  return strtmp;
}

ASN1_INTEGER *s2i_ASN1_INTEGER(const X509V3_EXT_METHOD *method,
                               const char *value) {
  BIGNUM *bn = NULL;
  ASN1_INTEGER *aint;
  int isneg, ishex;
  int ret;
  if (!value) {
    OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NULL_VALUE);
    return 0;
  }
  bn = BN_new();
  if (value[0] == '-') {
    value++;
    isneg = 1;
  } else {
    isneg = 0;
  }

  if (value[0] == '0' && ((value[1] == 'x') || (value[1] == 'X'))) {
    value += 2;
    ishex = 1;
  } else {
    ishex = 0;
  }

  if (ishex) {
    ret = BN_hex2bn(&bn, value);
  } else {
    // Decoding from decimal scales quadratically in the input length. Bound the
    // largest decimal input we accept in the config parser. 8,192 decimal
    // digits allows values up to 27,213 bits. Ths exceeds the largest RSA, DSA,
    // or DH modulus we support, and those are not usefully represented in
    // decimal.
    if (strlen(value) > 8192) {
      BN_free(bn);
      OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NUMBER);
      return 0;
    }
    ret = BN_dec2bn(&bn, value);
  }

  if (!ret || value[ret]) {
    BN_free(bn);
    OPENSSL_PUT_ERROR(X509V3, X509V3_R_BN_DEC2BN_ERROR);
    return 0;
  }

  if (isneg && BN_is_zero(bn)) {
    isneg = 0;
  }

  aint = BN_to_ASN1_INTEGER(bn, NULL);
  BN_free(bn);
  if (!aint) {
    OPENSSL_PUT_ERROR(X509V3, X509V3_R_BN_TO_ASN1_INTEGER_ERROR);
    return 0;
  }
  if (isneg) {
    aint->type |= V_ASN1_NEG;
  }
  return aint;
}

int X509V3_add_value_int(const char *name, const ASN1_INTEGER *aint,
                         STACK_OF(CONF_VALUE) **extlist) {
  char *strtmp;
  int ret;
  if (!aint) {
    return 1;
  }
  if (!(strtmp = i2s_ASN1_INTEGER(NULL, aint))) {
    return 0;
  }
  ret = X509V3_add_value(name, strtmp, extlist);
  OPENSSL_free(strtmp);
  return ret;
}

int X509V3_bool_from_string(const char *str, ASN1_BOOLEAN *out_bool) {
  if (!strcmp(str, "TRUE") || !strcmp(str, "true") || !strcmp(str, "Y") ||
      !strcmp(str, "y") || !strcmp(str, "YES") || !strcmp(str, "yes")) {
    *out_bool = ASN1_BOOLEAN_TRUE;
    return 1;
  }
  if (!strcmp(str, "FALSE") || !strcmp(str, "false") || !strcmp(str, "N") ||
      !strcmp(str, "n") || !strcmp(str, "NO") || !strcmp(str, "no")) {
    *out_bool = ASN1_BOOLEAN_FALSE;
    return 1;
  }
  OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_BOOLEAN_STRING);
  return 0;
}

int X509V3_get_value_bool(const CONF_VALUE *value, ASN1_BOOLEAN *out_bool) {
  const char *btmp = value->value;
  if (btmp == NULL) {
    OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_BOOLEAN_STRING);
    goto err;
  }
  if (!X509V3_bool_from_string(btmp, out_bool)) {
    goto err;
  }
  return 1;

err:
  X509V3_conf_err(value);
  return 0;
}

int X509V3_get_value_int(const CONF_VALUE *value, ASN1_INTEGER **aint) {
  ASN1_INTEGER *itmp;
  if (!(itmp = s2i_ASN1_INTEGER(NULL, value->value))) {
    X509V3_conf_err(value);
    return 0;
  }
  ASN1_INTEGER_free(*aint);
  *aint = itmp;
  return 1;
}

#define HDR_NAME 1
#define HDR_VALUE 2

// #define DEBUG

STACK_OF(CONF_VALUE) *X509V3_parse_list(const char *line) {
  char *p, *q, c;
  char *ntmp, *vtmp;
  STACK_OF(CONF_VALUE) *values = NULL;
  char *linebuf;
  int state;
  // We are going to modify the line so copy it first
  linebuf = OPENSSL_strdup(line);
  if (linebuf == NULL) {
    goto err;
  }
  state = HDR_NAME;
  ntmp = NULL;
  // Go through all characters
  for (p = linebuf, q = linebuf; (c = *p) && (c != '\r') && (c != '\n'); p++) {
    switch (state) {
      case HDR_NAME:
        if (c == ':') {
          state = HDR_VALUE;
          *p = 0;
          ntmp = strip_spaces(q);
          if (!ntmp) {
            OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NULL_NAME);
            goto err;
          }
          q = p + 1;
        } else if (c == ',') {
          *p = 0;
          ntmp = strip_spaces(q);
          q = p + 1;
#if 0
                printf("%s\n", ntmp);
#endif
          if (!ntmp) {
            OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NULL_NAME);
            goto err;
          }
          X509V3_add_value(ntmp, NULL, &values);
        }
        break;

      case HDR_VALUE:
        if (c == ',') {
          state = HDR_NAME;
          *p = 0;
          vtmp = strip_spaces(q);
#if 0
                printf("%s\n", ntmp);
#endif
          if (!vtmp) {
            OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NULL_VALUE);
            goto err;
          }
          X509V3_add_value(ntmp, vtmp, &values);
          ntmp = NULL;
          q = p + 1;
        }
    }
  }

  if (state == HDR_VALUE) {
    vtmp = strip_spaces(q);
#if 0
        printf("%s=%s\n", ntmp, vtmp);
#endif
    if (!vtmp) {
      OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NULL_VALUE);
      goto err;
    }
    X509V3_add_value(ntmp, vtmp, &values);
  } else {
    ntmp = strip_spaces(q);
#if 0
        printf("%s\n", ntmp);
#endif
    if (!ntmp) {
      OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NULL_NAME);
      goto err;
    }
    X509V3_add_value(ntmp, NULL, &values);
  }
  OPENSSL_free(linebuf);
  return values;

err:
  OPENSSL_free(linebuf);
  sk_CONF_VALUE_pop_free(values, X509V3_conf_free);
  return NULL;
}

// Delete leading and trailing spaces from a string
static char *strip_spaces(char *name) {
  char *p, *q;
  // Skip over leading spaces
  p = name;
  while (*p && OPENSSL_isspace((unsigned char)*p)) {
    p++;
  }
  if (!*p) {
    return NULL;
  }
  q = p + strlen(p) - 1;
  while ((q != p) && OPENSSL_isspace((unsigned char)*q)) {
    q--;
  }
  if (p != q) {
    q[1] = 0;
  }
  if (!*p) {
    return NULL;
  }
  return p;
}

// hex string utilities

char *x509v3_bytes_to_hex(const uint8_t *in, size_t len) {
  CBB cbb;
  if (!CBB_init(&cbb, len * 3 + 1)) {
    goto err;
  }
  for (size_t i = 0; i < len; i++) {
    static const char hex[] = "0123456789ABCDEF";
    if ((i > 0 && !CBB_add_u8(&cbb, ':')) ||
        !CBB_add_u8(&cbb, hex[in[i] >> 4]) ||
        !CBB_add_u8(&cbb, hex[in[i] & 0xf])) {
      goto err;
    }
  }
  uint8_t *ret;
  size_t unused_len;
  if (!CBB_add_u8(&cbb, 0) || !CBB_finish(&cbb, &ret, &unused_len)) {
    goto err;
  }

  return (char *)ret;

err:
  CBB_cleanup(&cbb);
  return NULL;
}

unsigned char *x509v3_hex_to_bytes(const char *str, size_t *len) {
  unsigned char *hexbuf, *q;
  unsigned char ch, cl, *p;
  uint8_t high, low;
  if (!str) {
    OPENSSL_PUT_ERROR(X509V3, X509V3_R_INVALID_NULL_ARGUMENT);
    return NULL;
  }
  if (!(hexbuf = OPENSSL_malloc(strlen(str) >> 1))) {
    goto err;
  }
  for (p = (unsigned char *)str, q = hexbuf; *p;) {
    ch = *p++;
    if (ch == ':') {
      continue;
    }
    cl = *p++;
    if (!cl) {
      OPENSSL_PUT_ERROR(X509V3, X509V3_R_ODD_NUMBER_OF_DIGITS);
      OPENSSL_free(hexbuf);
      return NULL;
    }
    if (!OPENSSL_fromxdigit(&high, ch)) {
      goto badhex;
    }
    if (!OPENSSL_fromxdigit(&low, cl)) {
      goto badhex;
    }
    *q++ = (high << 4) | low;
  }

  if (len) {
    *len = q - hexbuf;
  }

  return hexbuf;

err:
  OPENSSL_free(hexbuf);
  return NULL;

badhex:
  OPENSSL_free(hexbuf);
  OPENSSL_PUT_ERROR(X509V3, X509V3_R_ILLEGAL_HEX_DIGIT);
  return NULL;
}

int x509v3_conf_name_matches(const char *name, const char *cmp) {
  // |name| must begin with |cmp|.
  size_t len = strlen(cmp);
  if (strncmp(name, cmp, len) != 0) {
    return 0;
  }
  // |name| must either be equal to |cmp| or begin with |cmp|, followed by '.'.
  return name[len] == '\0' || name[len] == '.';
}

static int sk_strcmp(const char *const *a, const char *const *b) {
  return strcmp(*a, *b);
}

STACK_OF(OPENSSL_STRING) *X509_get1_email(const X509 *x) {
  GENERAL_NAMES *gens;
  STACK_OF(OPENSSL_STRING) *ret;

  gens = X509_get_ext_d2i(x, NID_subject_alt_name, NULL, NULL);
  ret = get_email(X509_get_subject_name(x), gens);
  sk_GENERAL_NAME_pop_free(gens, GENERAL_NAME_free);
  return ret;
}

STACK_OF(OPENSSL_STRING) *X509_get1_ocsp(const X509 *x) {
  AUTHORITY_INFO_ACCESS *info;
  STACK_OF(OPENSSL_STRING) *ret = NULL;
  size_t i;

  info = X509_get_ext_d2i(x, NID_info_access, NULL, NULL);
  if (!info) {
    return NULL;
  }
  for (i = 0; i < sk_ACCESS_DESCRIPTION_num(info); i++) {
    ACCESS_DESCRIPTION *ad = sk_ACCESS_DESCRIPTION_value(info, i);
    if (OBJ_obj2nid(ad->method) == NID_ad_OCSP) {
      if (ad->location->type == GEN_URI) {
        if (!append_ia5(&ret, ad->location->d.uniformResourceIdentifier)) {
          break;
        }
      }
    }
  }
  AUTHORITY_INFO_ACCESS_free(info);
  return ret;
}

STACK_OF(OPENSSL_STRING) *X509_REQ_get1_email(const X509_REQ *x) {
  GENERAL_NAMES *gens;
  STACK_OF(X509_EXTENSION) *exts;
  STACK_OF(OPENSSL_STRING) *ret;

  exts = X509_REQ_get_extensions(x);
  gens = X509V3_get_d2i(exts, NID_subject_alt_name, NULL, NULL);
  ret = get_email(X509_REQ_get_subject_name(x), gens);
  sk_GENERAL_NAME_pop_free(gens, GENERAL_NAME_free);
  sk_X509_EXTENSION_pop_free(exts, X509_EXTENSION_free);
  return ret;
}

static STACK_OF(OPENSSL_STRING) *get_email(const X509_NAME *name,
                                           const GENERAL_NAMES *gens) {
  STACK_OF(OPENSSL_STRING) *ret = NULL;
  // Now add any email address(es) to STACK
  int i = -1;
  // First supplied X509_NAME
  while ((i = X509_NAME_get_index_by_NID(name, NID_pkcs9_emailAddress, i)) >=
         0) {
    const X509_NAME_ENTRY *ne = X509_NAME_get_entry(name, i);
    const ASN1_IA5STRING *email = X509_NAME_ENTRY_get_data(ne);
    if (!append_ia5(&ret, email)) {
      return NULL;
    }
  }
  for (size_t j = 0; j < sk_GENERAL_NAME_num(gens); j++) {
    const GENERAL_NAME *gen = sk_GENERAL_NAME_value(gens, j);
    if (gen->type != GEN_EMAIL) {
      continue;
    }
    if (!append_ia5(&ret, gen->d.ia5)) {
      return NULL;
    }
  }
  return ret;
}

static void str_free(OPENSSL_STRING str) { OPENSSL_free(str); }

static int append_ia5(STACK_OF(OPENSSL_STRING) **sk,
                      const ASN1_IA5STRING *email) {
  // First some sanity checks
  if (email->type != V_ASN1_IA5STRING) {
    return 1;
  }
  if (email->data == NULL || email->length == 0) {
    return 1;
  }
  // |OPENSSL_STRING| cannot represent strings with embedded NULs. Do not
  // report them as outputs.
  if (OPENSSL_memchr(email->data, 0, email->length) != NULL) {
    return 1;
  }

  char *emtmp = NULL;
  if (!*sk) {
    *sk = sk_OPENSSL_STRING_new(sk_strcmp);
  }
  if (!*sk) {
    goto err;
  }

  emtmp = OPENSSL_strndup((char *)email->data, email->length);
  if (emtmp == NULL) {
    goto err;
  }

  // Don't add duplicates
  sk_OPENSSL_STRING_sort(*sk);
  if (sk_OPENSSL_STRING_find(*sk, NULL, emtmp)) {
    OPENSSL_free(emtmp);
    return 1;
  }
  if (!sk_OPENSSL_STRING_push(*sk, emtmp)) {
    goto err;
  }
  return 1;

err:
  // TODO(davidben): Fix the error-handling in this file. It currently relies
  // on |append_ia5| leaving |*sk| at NULL on error.
  OPENSSL_free(emtmp);
  X509_email_free(*sk);
  *sk = NULL;
  return 0;
}

void X509_email_free(STACK_OF(OPENSSL_STRING) *sk) {
  sk_OPENSSL_STRING_pop_free(sk, str_free);
}

typedef int (*equal_fn)(const unsigned char *pattern, size_t pattern_len,
                        const unsigned char *subject, size_t subject_len,
                        unsigned int flags);

// Compare while ASCII ignoring case.
static int equal_nocase(const unsigned char *pattern, size_t pattern_len,
                        const unsigned char *subject, size_t subject_len,
                        unsigned int flags) {
  if (pattern_len != subject_len) {
    return 0;
  }
  while (pattern_len) {
    unsigned char l = *pattern;
    unsigned char r = *subject;
    // The pattern must not contain NUL characters.
    if (l == 0) {
      return 0;
    }
    if (l != r) {
      if (OPENSSL_tolower(l) != OPENSSL_tolower(r)) {
        return 0;
      }
    }
    ++pattern;
    ++subject;
    --pattern_len;
  }
  return 1;
}

// Compare using OPENSSL_memcmp.
static int equal_case(const unsigned char *pattern, size_t pattern_len,
                      const unsigned char *subject, size_t subject_len,
                      unsigned int flags) {
  if (pattern_len != subject_len) {
    return 0;
  }
  return !OPENSSL_memcmp(pattern, subject, pattern_len);
}

// RFC 5280, section 7.5, requires that only the domain is compared in a
// case-insensitive manner.
static int equal_email(const unsigned char *a, size_t a_len,
                       const unsigned char *b, size_t b_len,
                       unsigned int unused_flags) {
  size_t i = a_len;
  if (a_len != b_len) {
    return 0;
  }
  // We search backwards for the '@' character, so that we do not have to
  // deal with quoted local-parts.  The domain part is compared in a
  // case-insensitive manner.
  while (i > 0) {
    --i;
    if (a[i] == '@' || b[i] == '@') {
      if (!equal_nocase(a + i, a_len - i, b + i, a_len - i, 0)) {
        return 0;
      }
      break;
    }
  }
  if (i == 0) {
    i = a_len;
  }
  return equal_case(a, i, b, i, 0);
}

// Compare the prefix and suffix with the subject, and check that the
// characters in-between are valid.
static int wildcard_match(const unsigned char *prefix, size_t prefix_len,
                          const unsigned char *suffix, size_t suffix_len,
                          const unsigned char *subject, size_t subject_len,
                          unsigned int flags) {
  const unsigned char *wildcard_start;
  const unsigned char *wildcard_end;
  const unsigned char *p;
  int allow_idna = 0;

  if (subject_len < prefix_len + suffix_len) {
    return 0;
  }
  if (!equal_nocase(prefix, prefix_len, subject, prefix_len, flags)) {
    return 0;
  }
  wildcard_start = subject + prefix_len;
  wildcard_end = subject + (subject_len - suffix_len);
  if (!equal_nocase(wildcard_end, suffix_len, suffix, suffix_len, flags)) {
    return 0;
  }
  // If the wildcard makes up the entire first label, it must match at
  // least one character.
  if (prefix_len == 0 && *suffix == '.') {
    if (wildcard_start == wildcard_end) {
      return 0;
    }
    allow_idna = 1;
  }
  // IDNA labels cannot match partial wildcards
  if (!allow_idna && subject_len >= 4 &&
      OPENSSL_strncasecmp((char *)subject, "xn--", 4) == 0) {
    return 0;
  }
  // The wildcard may match a literal '*'
  if (wildcard_end == wildcard_start + 1 && *wildcard_start == '*') {
    return 1;
  }
  // Check that the part matched by the wildcard contains only
  // permitted characters and only matches a single label.
  for (p = wildcard_start; p != wildcard_end; ++p) {
    if (!OPENSSL_isalnum(*p) && *p != '-') {
      return 0;
    }
  }
  return 1;
}

#define LABEL_START (1 << 0)
#define LABEL_END (1 << 1)
#define LABEL_HYPHEN (1 << 2)
#define LABEL_IDNA (1 << 3)

static const unsigned char *valid_star(const unsigned char *p, size_t len,
                                       unsigned int flags) {
  const unsigned char *star = 0;
  size_t i;
  int state = LABEL_START;
  int dots = 0;
  for (i = 0; i < len; ++i) {
    // Locate first and only legal wildcard, either at the start
    // or end of a non-IDNA first and not final label.
    if (p[i] == '*') {
      int atstart = (state & LABEL_START);
      int atend = (i == len - 1 || p[i + 1] == '.');
      // At most one wildcard per pattern.
      // No wildcards in IDNA labels.
      // No wildcards after the first label.
      if (star != NULL || (state & LABEL_IDNA) != 0 || dots) {
        return NULL;
      }
      // Only full-label '*.example.com' wildcards.
      if (!atstart || !atend) {
        return NULL;
      }
      star = &p[i];
      state &= ~LABEL_START;
    } else if (OPENSSL_isalnum(p[i])) {
      if ((state & LABEL_START) != 0 && len - i >= 4 &&
          OPENSSL_strncasecmp((char *)&p[i], "xn--", 4) == 0) {
        state |= LABEL_IDNA;
      }
      state &= ~(LABEL_HYPHEN | LABEL_START);
    } else if (p[i] == '.') {
      if ((state & (LABEL_HYPHEN | LABEL_START)) != 0) {
        return NULL;
      }
      state = LABEL_START;
      ++dots;
    } else if (p[i] == '-') {
      // no domain/subdomain starts with '-'
      if ((state & LABEL_START) != 0) {
        return NULL;
      }
      state |= LABEL_HYPHEN;
    } else {
      return NULL;
    }
  }

  // The final label must not end in a hyphen or ".", and
  // there must be at least two dots after the star.
  if ((state & (LABEL_START | LABEL_HYPHEN)) != 0 || dots < 2) {
    return NULL;
  }
  return star;
}

// Compare using wildcards.
static int equal_wildcard(const unsigned char *pattern, size_t pattern_len,
                          const unsigned char *subject, size_t subject_len,
                          unsigned int flags) {
  const unsigned char *star = NULL;

  // Subject names starting with '.' can only match a wildcard pattern
  // via a subject sub-domain pattern suffix match.
  if (!(subject_len > 1 && subject[0] == '.')) {
    star = valid_star(pattern, pattern_len, flags);
  }
  if (star == NULL) {
    return equal_nocase(pattern, pattern_len, subject, subject_len, flags);
  }
  return wildcard_match(pattern, star - pattern, star + 1,
                        (pattern + pattern_len) - star - 1, subject,
                        subject_len, flags);
}

int x509v3_looks_like_dns_name(const unsigned char *in, size_t len) {
  // This function is used as a heuristic for whether a common name is a
  // hostname to be matched, or merely a decorative name to describe the
  // subject. This heuristic must be applied to both name constraints and the
  // common name fallback, so it must be loose enough to accept hostname
  // common names, and tight enough to reject decorative common names.

  if (len > 0 && in[len - 1] == '.') {
    len--;
  }

  // Wildcards are allowed in front.
  if (len >= 2 && in[0] == '*' && in[1] == '.') {
    in += 2;
    len -= 2;
  }

  if (len == 0) {
    return 0;
  }

  size_t label_start = 0;
  for (size_t i = 0; i < len; i++) {
    unsigned char c = in[i];
    if (OPENSSL_isalnum(c) || (c == '-' && i > label_start) ||
        // These are not valid characters in hostnames, but commonly found
        // in deployments outside the Web PKI.
        c == '_' || c == ':') {
      continue;
    }

    // Labels must not be empty.
    if (c == '.' && i > label_start && i < len - 1) {
      label_start = i + 1;
      continue;
    }

    return 0;
  }

  return 1;
}

// Compare an ASN1_STRING to a supplied string. If they match return 1. If
// cmp_type > 0 only compare if string matches the type, otherwise convert it
// to UTF8.

static int do_check_string(const ASN1_STRING *a, int cmp_type, equal_fn equal,
                           unsigned int flags, int check_type, const char *b,
                           size_t blen, char **peername) {
  int rv = 0;

  if (!a->data || !a->length) {
    return 0;
  }
  if (cmp_type > 0) {
    if (cmp_type != a->type) {
      return 0;
    }
    if (cmp_type == V_ASN1_IA5STRING) {
      rv = equal(a->data, a->length, (unsigned char *)b, blen, flags);
    } else if (a->length == (int)blen && !OPENSSL_memcmp(a->data, b, blen)) {
      rv = 1;
    }
    if (rv > 0 && peername) {
      *peername = OPENSSL_strndup((char *)a->data, a->length);
      if (*peername == NULL) {
        return -1;
      }
    }
  } else {
    int astrlen;
    unsigned char *astr;
    astrlen = ASN1_STRING_to_UTF8(&astr, a);
    if (astrlen < 0) {
      return -1;
    }
    // We check the common name against DNS name constraints if it passes
    // |x509v3_looks_like_dns_name|. Thus we must not consider common names
    // for DNS fallbacks if they fail this check.
    if (check_type == GEN_DNS && !x509v3_looks_like_dns_name(astr, astrlen)) {
      rv = 0;
    } else {
      rv = equal(astr, astrlen, (unsigned char *)b, blen, flags);
    }
    if (rv > 0 && peername) {
      *peername = OPENSSL_strndup((char *)astr, astrlen);
      if (*peername == NULL) {
        return -1;
      }
    }
    OPENSSL_free(astr);
  }
  return rv;
}

static int do_x509_check(const X509 *x, const char *chk, size_t chklen,
                         unsigned int flags, int check_type, char **peername) {
  int cnid = NID_undef;
  int alt_type;
  int rv = 0;
  equal_fn equal;
  if (check_type == GEN_EMAIL) {
    cnid = NID_pkcs9_emailAddress;
    alt_type = V_ASN1_IA5STRING;
    equal = equal_email;
  } else if (check_type == GEN_DNS) {
    cnid = NID_commonName;
    alt_type = V_ASN1_IA5STRING;
    if (flags & X509_CHECK_FLAG_NO_WILDCARDS) {
      equal = equal_nocase;
    } else {
      equal = equal_wildcard;
    }
  } else {
    alt_type = V_ASN1_OCTET_STRING;
    equal = equal_case;
  }

  GENERAL_NAMES *gens = X509_get_ext_d2i(x, NID_subject_alt_name, NULL, NULL);
  if (gens) {
    for (size_t i = 0; i < sk_GENERAL_NAME_num(gens); i++) {
      const GENERAL_NAME *gen = sk_GENERAL_NAME_value(gens, i);
      if (gen->type != check_type) {
        continue;
      }
      const ASN1_STRING *cstr;
      if (check_type == GEN_EMAIL) {
        cstr = gen->d.rfc822Name;
      } else if (check_type == GEN_DNS) {
        cstr = gen->d.dNSName;
      } else {
        cstr = gen->d.iPAddress;
      }
      // Positive on success, negative on error!
      if ((rv = do_check_string(cstr, alt_type, equal, flags, check_type, chk,
                                chklen, peername)) != 0) {
        break;
      }
    }
    GENERAL_NAMES_free(gens);
    return rv;
  }

  // We're done if CN-ID is not pertinent
  if (cnid == NID_undef || (flags & X509_CHECK_FLAG_NEVER_CHECK_SUBJECT)) {
    return 0;
  }

  int j = -1;
  const X509_NAME *name = X509_get_subject_name(x);
  while ((j = X509_NAME_get_index_by_NID(name, cnid, j)) >= 0) {
    const X509_NAME_ENTRY *ne = X509_NAME_get_entry(name, j);
    const ASN1_STRING *str = X509_NAME_ENTRY_get_data(ne);
    // Positive on success, negative on error!
    if ((rv = do_check_string(str, -1, equal, flags, check_type, chk, chklen,
                              peername)) != 0) {
      return rv;
    }
  }
  return 0;
}

int X509_check_host(const X509 *x, const char *chk, size_t chklen,
                    unsigned int flags, char **peername) {
  if (chk == NULL) {
    return -2;
  }
  if (OPENSSL_memchr(chk, '\0', chklen)) {
    return -2;
  }
  return do_x509_check(x, chk, chklen, flags, GEN_DNS, peername);
}

int X509_check_email(const X509 *x, const char *chk, size_t chklen,
                     unsigned int flags) {
  if (chk == NULL) {
    return -2;
  }
  if (OPENSSL_memchr(chk, '\0', chklen)) {
    return -2;
  }
  return do_x509_check(x, chk, chklen, flags, GEN_EMAIL, NULL);
}

int X509_check_ip(const X509 *x, const unsigned char *chk, size_t chklen,
                  unsigned int flags) {
  if (chk == NULL) {
    return -2;
  }
  return do_x509_check(x, (const char *)chk, chklen, flags, GEN_IPADD, NULL);
}

int X509_check_ip_asc(const X509 *x, const char *ipasc, unsigned int flags) {
  unsigned char ipout[16];
  size_t iplen;

  if (ipasc == NULL) {
    return -2;
  }
  iplen = (size_t)x509v3_a2i_ipadd(ipout, ipasc);
  if (iplen == 0) {
    return -2;
  }
  return do_x509_check(x, (const char *)ipout, iplen, flags, GEN_IPADD, NULL);
}

// Convert IP addresses both IPv4 and IPv6 into an OCTET STRING compatible
// with RFC 3280.

ASN1_OCTET_STRING *a2i_IPADDRESS(const char *ipasc) {
  unsigned char ipout[16];
  ASN1_OCTET_STRING *ret;
  int iplen;

  iplen = x509v3_a2i_ipadd(ipout, ipasc);
  if (!iplen) {
    return NULL;
  }

  ret = ASN1_OCTET_STRING_new();
  if (!ret) {
    return NULL;
  }
  if (!ASN1_OCTET_STRING_set(ret, ipout, iplen)) {
    ASN1_OCTET_STRING_free(ret);
    return NULL;
  }
  return ret;
}

ASN1_OCTET_STRING *a2i_IPADDRESS_NC(const char *ipasc) {
  ASN1_OCTET_STRING *ret = NULL;
  unsigned char ipout[32];
  char *iptmp = NULL, *p;
  int iplen1, iplen2;
  p = strchr(ipasc, '/');
  if (!p) {
    return NULL;
  }
  iptmp = OPENSSL_strdup(ipasc);
  if (!iptmp) {
    return NULL;
  }
  p = iptmp + (p - ipasc);
  *p++ = 0;

  iplen1 = x509v3_a2i_ipadd(ipout, iptmp);

  if (!iplen1) {
    goto err;
  }

  iplen2 = x509v3_a2i_ipadd(ipout + iplen1, p);

  OPENSSL_free(iptmp);
  iptmp = NULL;

  if (!iplen2 || (iplen1 != iplen2)) {
    goto err;
  }

  ret = ASN1_OCTET_STRING_new();
  if (!ret) {
    goto err;
  }
  if (!ASN1_OCTET_STRING_set(ret, ipout, iplen1 + iplen2)) {
    goto err;
  }

  return ret;

err:
  OPENSSL_free(iptmp);
  ASN1_OCTET_STRING_free(ret);
  return NULL;
}

int x509v3_a2i_ipadd(unsigned char ipout[16], const char *ipasc) {
  // If string contains a ':' assume IPv6

  if (strchr(ipasc, ':')) {
    if (!ipv6_from_asc(ipout, ipasc)) {
      return 0;
    }
    return 16;
  } else {
    if (!ipv4_from_asc(ipout, ipasc)) {
      return 0;
    }
    return 4;
  }
}

static int ipv4_from_asc(unsigned char v4[4], const char *in) {
  int a0, a1, a2, a3;
  if (sscanf(in, "%d.%d.%d.%d", &a0, &a1, &a2, &a3) != 4) {
    return 0;
  }
  if ((a0 < 0) || (a0 > 255) || (a1 < 0) || (a1 > 255) || (a2 < 0) ||
      (a2 > 255) || (a3 < 0) || (a3 > 255)) {
    return 0;
  }
  v4[0] = a0;
  v4[1] = a1;
  v4[2] = a2;
  v4[3] = a3;
  return 1;
}

typedef struct {
  // Temporary store for IPV6 output
  unsigned char tmp[16];
  // Total number of bytes in tmp
  int total;
  // The position of a zero (corresponding to '::')
  int zero_pos;
  // Number of zeroes
  int zero_cnt;
} IPV6_STAT;

static int ipv6_from_asc(unsigned char v6[16], const char *in) {
  IPV6_STAT v6stat;
  v6stat.total = 0;
  v6stat.zero_pos = -1;
  v6stat.zero_cnt = 0;
  // Treat the IPv6 representation as a list of values separated by ':'.
  // The presence of a '::' will parse as one, two or three zero length
  // elements.
  if (!CONF_parse_list(in, ':', 0, ipv6_cb, &v6stat)) {
    return 0;
  }

  if (v6stat.zero_pos == -1) {
    // If no '::' must have exactly 16 bytes
    if (v6stat.total != 16) {
      return 0;
    }
  } else {
    // If '::' must have less than 16 bytes
    if (v6stat.total >= 16) {
      return 0;
    }
    if (v6stat.zero_cnt > 3) {
      // More than three zeroes is an error
      return 0;
    } else if (v6stat.zero_cnt == 3) {
      // Can only have three zeroes if nothing else present
      if (v6stat.total > 0) {
        return 0;
      }
    } else if (v6stat.zero_cnt == 2) {
      // Can only have two zeroes if at start or end
      if (v6stat.zero_pos != 0 && v6stat.zero_pos != v6stat.total) {
        return 0;
      }
    } else {
      // Can only have one zero if *not* start or end
      if (v6stat.zero_pos == 0 || v6stat.zero_pos == v6stat.total) {
        return 0;
      }
    }
  }

  // Format the result.
  if (v6stat.zero_pos >= 0) {
    // Copy initial part
    OPENSSL_memcpy(v6, v6stat.tmp, v6stat.zero_pos);
    // Zero middle
    OPENSSL_memset(v6 + v6stat.zero_pos, 0, 16 - v6stat.total);
    // Copy final part
    if (v6stat.total != v6stat.zero_pos) {
      OPENSSL_memcpy(v6 + v6stat.zero_pos + 16 - v6stat.total,
                     v6stat.tmp + v6stat.zero_pos,
                     v6stat.total - v6stat.zero_pos);
    }
  } else {
    OPENSSL_memcpy(v6, v6stat.tmp, 16);
  }

  return 1;
}

static int ipv6_cb(const char *elem, size_t len, void *usr) {
  IPV6_STAT *s = usr;
  // Error if 16 bytes written
  if (s->total == 16) {
    return 0;
  }
  if (len == 0) {
    // Zero length element, corresponds to '::'
    if (s->zero_pos == -1) {
      s->zero_pos = s->total;
    } else if (s->zero_pos != s->total) {
      // If we've already got a :: its an error
      return 0;
    }
    if (s->zero_cnt >= 3) {
      // More than three zeros is an error.
      return 0;
    }
    s->zero_cnt++;
  } else {
    // If more than 4 characters could be final a.b.c.d form
    if (len > 4) {
      // Need at least 4 bytes left
      if (s->total > 12) {
        return 0;
      }
      // Must be end of string
      if (elem[len]) {
        return 0;
      }
      if (!ipv4_from_asc(s->tmp + s->total, elem)) {
        return 0;
      }
      s->total += 4;
    } else {
      if (!ipv6_hex(s->tmp + s->total, elem, len)) {
        return 0;
      }
      s->total += 2;
    }
  }
  return 1;
}

// Convert a string of up to 4 hex digits into the corresponding IPv6 form.

static int ipv6_hex(unsigned char *out, const char *in, size_t inlen) {
  if (inlen > 4) {
    return 0;
  }
  uint16_t num = 0;
  while (inlen--) {
    uint8_t val;
    if (!OPENSSL_fromxdigit(&val, *in++)) {
      return 0;
    }
    num = (num << 4) | val;
  }
  out[0] = num >> 8;
  out[1] = num & 0xff;
  return 1;
}

int X509V3_NAME_from_section(X509_NAME *nm, const STACK_OF(CONF_VALUE) *dn_sk,
                             int chtype) {
  if (!nm) {
    return 0;
  }

  for (size_t i = 0; i < sk_CONF_VALUE_num(dn_sk); i++) {
    const CONF_VALUE *v = sk_CONF_VALUE_value(dn_sk, i);
    const char *type = v->name;
    // Skip past any leading X. X: X, etc to allow for multiple instances
    for (const char *p = type; *p; p++) {
      if ((*p == ':') || (*p == ',') || (*p == '.')) {
        p++;
        if (*p) {
          type = p;
        }
        break;
      }
    }
    int mval;
    if (*type == '+') {
      mval = -1;
      type++;
    } else {
      mval = 0;
    }
    if (!X509_NAME_add_entry_by_txt(nm, type, chtype, (unsigned char *)v->value,
                                    -1, -1, mval)) {
      return 0;
    }
  }
  return 1;
}